Luciane Ayres-Peres

Natural diet of the freshwater anomuran Aegla longirostri (Crustacea, Anomura, Aeglidae)

The present study characterized the diet of Aegla longirostri from southern Brazil, in relation to seasonality, size and sex of the animals. The aeglids were sampled bimonthly, from October 1999 to August 2000. The animals were dissected and the Stomach Repletion Degree (RD) and the food items contained in each stomach were recorded. For each food item with RD⩾0.5, the Relative Importance Index (RII) was calculated. Of 399 animals collected, 305 had RD⩾0.5. The following items were found in the stomachs: plant tissue, non‐identified material, sediment, and fragments of adult insects, as well as fragments of Aegla sp., mollusc shells, fish scales and dipteran larvae. Independently of size class and sex, the animals showed a preference for plant tissue. These results demonstrate that A. longirostri has an omnivorous feeding habit, and is mainly herbivorous.

Description of the Agonistic Behavior of Aegla longirostri (Decapoda: Aeglidae)

Abstract Among animals, conflicts are resolved through agonistic behavior, an expression of which embraces a range of fleeing behaviors, displays, up to the extreme of physical combat. This study aims to establish an observation protocol and to describe the aggressive acts of Aegla longirostri. Aeglids were collected in the field and kept for one week of acclimation in individual fishbowls with no contact with other animals. A total of ten pairs of males were paired, the members of each pair differing by no more than 1 mm in cephalothorax length. The behavioral acts were described from the combats videotaped for 20 minutes with each pair, of which 16 were considered aggressive acts. The animals took an average of 198 seconds to start combat. A table of aggression intensity was established, ranging from −2 (fleeing) to 5 (intense combat). There was a significant difference between winners and losers in the time spent in the different levels of intensity and in the duration of the acts performed. Aegla longirostri showed very intense aggression with defined aggressive acts and continued to engage in agonistic behavior for the entire duration that was recorded. This is the first report of aggressive behavior in aeglids, it will be possible to carry out more profound studies on the behavior of these animals.

Atividade nictimeral e tempo de digestão de Aegla longirostri (Crustacea, Decapoda, Anomura)

The aim of this work was to characterize the diel activity rhythm and time of digestion in Aegla longirostri Bond-Buckup & Buckup, 1994. The individuals were collected in Santa Maria, RS, Brazil. In laboratory, the animals were kept in individuals glass aquariums (5L). To test locomotor and feeding activity of the aeglids, a group remained under constant luminosity for 12 hours, while another group was mantained in the dark, this condition being reversed at each 12 hours. The observations were taken at every 6 hours. For the determination of digestions time the animals were fed, and one individual was sacrificed at each 30 minutes. Aegla longirostri showed lower activity in periods of light time. This condition was recorded for both groups of animals. This species takes approximately 5 hours to conclude its extracellular digestion. The results suggest that A. longirostri has nocturnal habits and probably feeds whenever resources are available.

Modulation of male aggressiveness through different communication pathways

Communication plays a large role in resource competition, especially for potential mates, and is used by members of the competing sex to assess each other, and simultaneously to evaluate the other sex, which may be advertising its status. To assess the effects of female advertisement on male aggression, males of the decapod Aegla were paired according to body and armament size. Males were left to interact in five different treatments: with receptive females that could use both chemical and visual cues, non-receptive females that could use both types of cues, receptive females that could use only one cue, or no female in the aquarium. Fight duration, time spent in the most aggressive acts, latency period, number of antennal whips/fight duration, and time spent near the female were analyzed. The males had shorter and less intense confrontations when there was a receptive female that could signal with at least one modality. Winning males spent significantly more time near the receptive female only when both chemical and visual cues were present, when compared to the other treatments. The low level of aggression shown by the males may be related to information asymmetry due to the female’s choice: only the preferred male would receive information from the female, or males could compete for other resources that attract females. However, male aggression was modified by the presence of female chemical cues, whereas mate guarding was initiated only when both chemical and visual cues were present. Hence, male aggression can be downregulated by female receptivity.

Ocupação de conchas de gastrópodes por ermitões (Decapoda, Anomura) no litoral de Rio Grande, Rio Grande do Sul, Brasil

O presente estudo teve como objetivo caracterizar a ocupacao de conchas por ermitoes no litoral da cidade de Rio Grande, Estado do Rio Grande do Sul. Os animais foram amostrados em 14 radiais em Rio Grande, entre 12 e 50 metros de profundidade. Cada ermitao e sua respectiva concha foram identificados, pesados e medidos. Um total de 408 animais foi capturado, pertencentes as familias Diogenidae e Paguridae; as duas especies mais abundantes foram Dardanus insignis (de Saussure, 1858) e Loxopagurus loxochelis (Moreira, 1901). Os ermitoes ocuparam conchas de 13 especies de gastropodes, principalmente de Buccinanops lamarckii (Kiener, 1834) e B. gradatum (Deshayes, 1844). Dardanus insignis utilizou 12 das 13 especies de moluscos registradas; Loxopagurus loxochelis utilizou nove. De um modo geral, o padrao de ocupacao de conchas apresenta uma correlacao entre o tamanho do ermitao e o tamanho da concha; no caso das duas especies de ermitoes mais abundantes, a maior correlacao foi entre peso/tamanho do animal e o tamanho da abertura da concha, evidenciando, que a ocupacao de conchas se da nao apenas pela disponibilidade local das mesmas, mas tambem pelas relacoes entre as variaveis dos ermitoes e das conchas de gastropodes.

Radio-telemetry techniques in the study of displacement of freshwater anomurans

In an ecological context, information on the movement and activity is important for understanding the requirements of habitat, resource usage patterns and the potential of interspecific interactions. The aim of this study was to examine the displacement pattern on daily activity and occupancy of substrates by Aegla manuinflata using radio-telemetry technique on field on Southern Brazil. Four adult males were monitored during nine days. The aeglids showed a significantly greater displacement toward upstream than downstream. Aegla manuinflata individuals showed higher displacement activity during the night period. Although activity was not constant: the animals spent one or more days without displacement. All aeglids showed locomotion activity concentrated between 11:43 p.m. and 02:25 a.m., although it was not restrict to sunset period and night. Individuals showed specific occupation of different types of substrate, but a pattern in the occupation of substrates as a function of the photoperiod was not observed. In this study, using a new technique for tracking aeglids, it was concluded that A. manuinflata is capable of actively dislocate throughout the stream, either toward upstream and downstream, passing through obstacles which may represent ability of re-colonization. The animals are more active during the night period, probably a strategy to avoid predators that are active during the day; the selection of substrate is not associated to sediment texture.

Diversity and abundance of the benthic macrofauna in lotic environments from the central region of Rio Grande do Sul state, Brazil

The benthic fauna plays an important role in the trophic web and the nutrient flow of limnetic environments. This work aimed to study the diversity and abundance of the benthic invertebrates in four watercourses in the central region of the state of Rio Grande do Sul, Brazil. Sampling was done seasonally at each site, with a long-handled net at the margins (banks) and streambed, from November 2001 through September 2002. Margalef richness, Shannon diversity and Pielou evenness indices were applied to the data analysis. A total of 58 families and three other major taxa (Hirudinea, Oligochaeta and Copepoda) of invertebrates were identified. The highest values of diversity and abundance were recorded at the margins of the rivers, in the same pattern found in other tropical and subtropical regions. This is the first inventory of benthic invertebrates from central region of Rio Grande do Sul, which will be important for future studies of the diversity and conservation of this fauna, because human alterations of the environment have already begun.

Thanatosis in freshwater anomurans (Decapoda: Aeglidae)

The present study evaluated the occurrence of thanatosis in freshwater crustaceans. The duration of the thanatosis events was compared with respect to photoperiod and size for Aegla longirostri (Brazil) and Aegla denticulata denticulata (Chile). Adults of A. longirostri did not show thanatosis; juveniles were responsive only when they were out of water. In the two species, thanatosis occurred in both light and dark photophases, and there was no significant difference in the duration of the events between the photophases. For A. d. denticulata, which lives in deep waters and in sympatry with larger decapods, this behaviour seems to represent an adaptation either to the environment or to the biotic community of the species. This behaviour is apparently not necessary for adults of A. longirostri, since this species is mainly nocturnal in its adult phase and its activity rhythms do not coincide with those of its potential predators.